Authentication technologies utilizing a living body as authentication means are coming into wide use. And, incorporating biometric authentication into a potable communication device, such as a cellular phone, enables authentication processing to be easily performed on a communication party anywhere through the portable communication device, so it is important to incorporate a biometric authentication apparatus into a portable communication device. Reduction in size and increase in density of a portable communication device in recent years are drastic, so size reduction in an incorporated apparatus is an important issue.
Traditionally, there are vein authentication apparatuses utilizing a vein as a target, and one example of such vein authentication apparatuses is a vein authentication apparatus called the transmissive type. For the vein authentication apparatus of this transmissive type, a light illuminating portion and an imaging portion are disposed so as to sandwich a finger containing a vein being an authentication target, and it is illuminated with near-infrared light from behind the vein. Owing to this, a non-vein section is in a light state, whereas a vein section is maintained in a dark state because of absorption properties of hemoglobin. This leads to a sharp contrast between the vein section and the non-vein section, and therefore, a good vein image is obtainable.
However, for the vein authentication apparatus of the transmissive type, the light illuminating portion and the imaging portion are disposed so as to sandwich a finger, and typically, the finger sandwiched between the light illuminating portion and the imaging portion is covered with a blocking portion for blocking light other than imaging light. This may cause problems in which an authentication-target person feels uneasy about the finger being covered and the apparatus has a large size. One example that can solve these problems is a vein authentication apparatus of the reflective scattering type (refer to Patent Document 1).
For the vein authentication apparatus of this reflective scattering type, a light illuminating portion and an imaging portion are disposed on the same direction side with respect to a finger containing a vein being an authentication target, and the finger is not covered with a blocking portion, and it is illuminated with near-infrared light from behind the vein. Owing to this, as compared with a vein authentication apparatus of the transmissive type, ease can be offered to an authentication-target person and size reduction can be achieved. Additionally, owing to the production of scattering light behind a vein plexus being an authentication target, a non-vein section is in a light state, whereas a vein section is maintained in a dark state because of absorption properties of hemoglobin, so a vein image having a good contrast is obtainable.    Patent Document 1: International Publication No. 03-096272
However, in the case where the light illuminating portion and the imaging portion are disposed on the same direction side with respect to the finger being an authentication target, in order to prevent light from entering the gap between a vein plexus being an imaging target and the imaging portion, it is necessary to largely incline near-infrared light to be output toward the vein plexus. Because of this, there is a problem in which the apparatus has a large size.